Increased capsaicin cough sensitivity in patients with multiple chemical sensitivity

Multiple Chemical Sensitivity: It's time to catch up to the science

Multiple chemical sensitivity (MCS) is a complex medical condition associated with low dose chemical exposures. MCS is characterized by diverse features and common comorbidities, including fibromyalgia, cough hypersensitivity, asthma, and migraine, and stress/anxiety, with which the syndrome shares numerous neurobiological processes and altered functioning within diverse brain regions. Predictive factors linked to MCS comprise genetic influences, gene-environment interactions, oxidative stress, systemic inflammation, cell dysfunction, and psychosocial influences. The development of MCS may be attributed to the sensitization of transient receptor potential (TRP) receptors, notably TRPV1 and TRPA1. Capsaicin inhalation challenge studies demonstrated that TRPV1 sensitization is manifested in MCS, and functional brain imaging studies revealed that TRPV1 and TRPA1 agonists promote brain-region specific neuronal variations. Unfortunately, MCS has often been inappropriately viewed as stemming exclusively from psychological disturbances, which has fostered patients being stigmatized and ostracized, and often being denied accommodation for their disability. Evidence-based education is essential to provide appropriate support and advocacy. Greater recognition of receptor-mediated biological mechanisms should be incorporated in laws, and regulation of environmental exposures.

Neurological susceptibility to environmental exposures: pathophysiological mechanisms in neurodegeneration and multiple chemical sensitivity

The World Health Organization lists air pollution as one of the top five risks for developing chronic non-communicable disease, joining tobacco use, harmful use of alcohol, unhealthy diets and physical inactivity. This review focuses on how host defense mechanisms against adverse airborne exposures relate to the probable interacting and overlapping pathophysiological features of neurodegeneration and multiple chemical sensitivity. Significant long-term airborne exposures can contribute to oxidative stress, systemic inflammation, transient receptor subfamily vanilloid 1 (TRPV1) and subfamily ankyrin 1 (TRPA1) upregulation and sensitization, with impacts on olfactory and trigeminal nerve function, and eventual loss of brain mass. The potential for neurologic dysfunction, including decreased cognition, chronic pain and central sensitization related to airborne contaminants, can be magnified by genetic polymorphisms that result in less effective detoxification. Onset of neurodegenerative disorders is subtle, with early loss of brain mass and loss of sense of smell. Onset of MCS may be gradual following long-term low dose airborne exposures, or acute following a recognizable exposure. Upregulation of chemosensitive TRPV1 and TRPA1 polymodal receptors has been observed in patients with neurodegeneration, and chemically sensitive individuals with asthma, migraine and MCS. In people with chemical sensitivity, these receptors are also sensitized, which is defined as a reduction in the threshold and an increase in the magnitude of a response to noxious stimulation. There is likely damage to the olfactory system in neurodegeneration and trigeminal nerve hypersensitivity in MCS, with different effects on olfactory processing. The associations of low vitamin D levels and protein kinase activity seen in neurodegeneration have not been studied in MCS. Table 2 presents a summary of neurodegeneration and MCS, comparing 16 distinctive genetic, pathophysiological and clinical features associated with air pollution exposures. There is significant overlap, suggesting potential comorbidity. Canadian Health Measures Survey data indicates an overlap between neurodegeneration and MCS (p < 0.05) that suggests comorbidity, but the extent of increased susceptibility to the other condition is not established. Nevertheless, the pathways to the development of these conditions likely involve TRPV1 and TRPA1 receptors, and so it is hypothesized that manifestation of neurodegeneration and/or MCS and possibly why there is divergence may be influenced by polymorphisms of these receptors, among other factors.

Evaluation methods and influencing factors of cough sensitivity

Increased cough sensitivity is an important mechanism of chronic cough, and the evaluation of cough sensitivity helps understand the mechanism of cough and explore better methods to reduce cough. Evaluation methods may be direct or indirect. Direct methods include mechanical stimulation and chemical stimulation, and indirect methods include laryngeal reflex test, questionnaires, and brain functional magnetic resonance imaging (fMRI). Chemical stimulation is the most common method, while the capsaicin cough challenge test is proven and widely used. In this article, we will compare evaluation methods and explore influencing factors of cough sensitivity.

Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives

OBJECTIVE

Systematic bibliography analysis of about the last 17 years on multiple chemical sensitivity (MCS) was carried out in order to detect new diagnostic and epidemiological evidence. The MCS is a complex syndrome that manifests as a result of exposure to a low level of various common contaminants. The etiology, diagnosis, and treatment are still debated among researchers.

METHOD

Querying PubMed, Web of Science, Scopus, Cochrane library, both using some specific MESH terms combined with MESH subheadings and through free search, even by Google.

RESULTS

The studies were analyzed by verifying 1) the typology of study design; 2) criteria for case definition; 3) presence of attendances in the emergency departments and hospital admissions, and 4) analysis of the risk factors.

OUTLOOK

With this review, we give some general considerations and hypothesis for possible future research.

Symptoms from masked acrolein exposure suggest altered trigeminal reactivity in chemical intolerance

BACKGROUND

Chemical intolerance (CI) is a widespread occupational and public health problem characterized by symptoms that reportedly result from low-levels of chemical exposure. The mechanisms behind CI are unknown, however modifications of the chemical senses (rather than toxic processes) have been suggested as key components. The aim of this study was to investigate whether individuals with self-reported CI report more sensory irritation during masked acrolein exposure compared to controls without CI.

METHODS

Individuals with CI (n=18) and controls without CI (n=19) were exposed in an exposure chamber. Each participant took part in two exposure conditions - one with heptane (the masking compound), and one with heptane and acrolein at a dose below previously reported sensory irritation thresholds. The exposures lasted for 60min. Symptoms and confidence ratings were measured continuously throughout the exposure as were measurements of electrodermal activity and self-reported tear-film break-up time. Participants were blind to exposure condition.

RESULTS

Individuals with CI, compared with controls reported greater sensory irritation in the eyes, nose and throat when exposed to acrolein masked with heptane. There was no difference during exposure to heptane.

CONCLUSIONS

Masked exposure to acrolein at a concentration below the previously reported detection threshold is perceived as more irritating by individuals with CI compared with controls. The results indicate that there is altered trigeminal reactivity in those with CI compared to controls.

Long-Term Follow-Up in Patients With Airway Chemical Intolerance

OBJECTIVE

A 5-year follow-up study showed that a group of patients with airway symptoms from chemicals and scents had lasting symptoms, together with enduring increased capsaicin cough sensitivity. The aim was to follow up the same patients after another 5 years.

METHODS

All previously participants were invited for an additional follow-up. They visited the clinic twice; at one opportunity, they undertook a capsaicin inhalation provocation, and at the other, a methacholine provocation, and answered various questionnaires.

RESULTS

Sixteen patients attende the study after a median of 8 years. They reported unchanged symptoms from chemicals and scents; the capsaicin cough sensitivity was still increased, and the repeatability for the capsaicin inhalation was good.

CONCLUSIONS

Airway symptoms induced by chemicals and scents constitute a chronic disease, with unchanged trigger factors, persistent symptoms, and unchanged, long-lasting sensory hyperreactivity.All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.This study was supported by grants from the Herman Krefting Foundation Against Asthma/Allergy, the Swedish Heart and Lung Foundation, and the Swedish Cancer and Allergy Fund.

Capsaicin sensitivity in patients with chronic cough- results from a cross-sectional study

Background

A subgroup of patients with chronic cough is recognised as having airway symptoms resulting exposure to chemicals and scents related to enhanced cough sensitivity to inhaled capsaicin. Sensory hyperreactivity, which has an estimated prevalence of more than 6%, is one possible explanation for the symptoms experienced by these patients. We hypothesized that a number of patients diagnosed with chronic unexplained cough also have coughing provoked by chemical irritants associated with augmented capsaicin cough reaction, but the extent of such a relation is not known. One aim of the present study was to analyse cough sensitivity to inhaled capsaicin in patients with chronic unexplained cough. Another aim was to compare capsaicin sensitivity in individuals with chemically induced coughing (the chemical-sensitive group) to capsaicin sensitivity in those without such chemical sensitivity (non-sensitive group).

Methods

Fifty-six participants from an earlier cross-sectional study of 62 patients with chronic unexplained cough were asked to participate in this study: 33 were chemical-sensitive and 23 were non-sensitive. Each participant visited the clinic once and performed a capsaicin inhalation test with one of two inhalation devices. The number of coughs, induced airway symptoms, and spirometry results were recorded.

Results

Thirty-nine of the invited patients participated in the study, with 32 in the chemical-sensitive group (21 women, 11 men), and 7 in the non-sensitive group (4 women, 3 men). The chemical-sensitive patients coughed significantly more on inhaling capsaicin, and had significantly more other airway symptoms compared to those in the non-sensitive group. Women coughed significantly more than men after receiving the higher concentration of capsaicin.

Conclusions

Environmental irritants often trigger chronic unexplained cough. The current findings confirm that this sensitivity is related to enhanced capsaicin cough sensitivity and indicates more involvement of airway sensory nerves in the pathophysiology of the disease than in cough without evident trigger factors.

Review of evidence for a toxicological mechanism of idiopathic environmental intolerance

Idiopathic environmental intolerance (IEI) is a medically unexplained disorder characterised by a wide variety of unspecific symptoms in different organ systems and attributed to nontoxic concentrations of chemicals and other environmental factors that are tolerated by the majority of individuals. Both exposure to chemicals and behavioural conditioning are considered as possible contributors to the development of IEI. However, owing to the heterogeneity of the condition, it is difficult to separate the toxicological, physiological and psychological aspects of IEI. Here, we review the evidence for postulated toxicologically mediated mechanisms for IEI. Available data do not support either a classical receptor-mediated or an idiosyncratic toxicological mechanism. Furthermore, if there were convincing evidence for a psychological cause for many patients with IEI, then this would suggest that the priority for the future is the development of psychological treatments for IEI. Finally, we advocate genome wide screening of IEI patients to elucidate genotypic features of the condition.

Diagnosis of asthma - a new approach

Current definition of asthma involves four cornerstones: inflammation, hyperresponsiveness, bronchoconstriction, and symptoms. In research, the symptoms have had the slightest attention. According to international guidelines, the asthma symptoms are episodic breathlessness, wheeze, cough, tightness of the chest, and shortness of breath. As there are several symptoms, a primary question is how they are related to bronchoconstriction, the main clinical feature of asthma. Symptoms and lung function tests are regularly used for the evaluation of clinical health status and effect of treatment. However, there is no or poor correlation between these two variables, which means that they represent different mechanisms. Reduced lung function, such as a low FEV(1) , represents bronchial constriction, what do the symptoms represent? Some symptoms such as breathlessness and shortness of breath seem not to be evidence-based asthma symptoms. Focusing on bronchial obstruction is important in view of the potential risk of asthma attacks, but nonobstructive symptoms occur frequently and may also cause severe discomfort and poor quality of life. Interpreting all symptoms as signs of bronchoconstriction (asthma) may lead to misinterpretation when assessing health status and effect of treatment. Although a 'soft' variable, the strength of symptoms is that they are representing various mechanisms. The physiological preconditions for control and defense of respiration must be considered in the diagnostic process, regardless of inflammation, allergy, psychology, or other etiological factors. Based on studies on dyspnea in cardiopulmonary diseases, including asthma and asthma-like disorders, there seems to be a continuous spectrum of symptoms and mechanisms integrated in a single asthma syndrome.

TRPA1 receptors mediate environmental irritant-induced meningeal vasodilatation

The TRPA1 receptor is a member of the transient receptor potential (TRP) family of ion channels expressed in nociceptive neurons. TRPA1 receptors are targeted by pungent compounds from mustard and garlic and environmental irritants such as formaldehyde and acrolein. Ingestion or inhalation of these chemical agents causes irritation and burning in the nasal and oral mucosa and respiratory lining. Headaches have been widely reported to be induced by inhalation of environmental irritants, but it is unclear how these agents produce headache. Stimulation of trigeminal neurons releases CGRP and substance P and induces neurogenic inflammation associated with the pain of migraine. Here we test the hypothesis that activation of TRPA1 receptors is the mechanistic link between environmental irritants and peptide-mediated neurogenic inflammation. Known TRPA1 agonists and environmental irritants stimulate CGRP release from dissociated rat trigeminal ganglia neurons and this release is blocked by a selective TRPA1 antagonist, HC-030031. Further, TRPA1 agonists and environmental irritants increase meningeal blood flow following intranasal administration. Prior dural application of the CGRP antagonist, CGRP(8-37), or intranasal or dural administration of HC-030031, blocks the increases in blood flow elicited by environmental irritants. Together these results demonstrate that TRPA1 receptor activation by environmental irritants stimulates CGRP release and increases cerebral blood flow. We suggest that these events contribute to headache associated with environmental irritants.

The airway sensory hyperreactivity syndrome

After exclusion of diverse pulmonary illnesses, the remaining explanations for chronic cough include medication with angiotensin-converting enzyme (ACE) inhibitor, gastroesophageal reflux disease (GERD), and post-nasal drip. Different clinics report shifting frequencies for both the causes of chronic cough and the success of treatment. However, after all evaluations, differential diagnosis still leaves a group of patients with unexplained cough. This unexplained cough is also known as chronic idiopathic cough (CIC), though there are widely varying opinions as to its existence. Among patients previously diagnosed with CIC, a subgroup has been identified with both upper and lower airway symptoms, including cough induced by odours and chemicals, and with increased cough sensitivity to inhaled capsaicin, which is known to stimulate the airway sensory nerves. A suggested explanation for this condition is a hyperreactivity of the sensory nerves of the entire airways, and hence the condition is known as sensory hyperreactivity (SHR). SHR affects more than 6% of the adult population in Sweden. It is a longstanding condition, and is clearly associated with significant social and psychological impacts.

Up-regulation of neurotrophin-related gene expression in mouse hippocampus following low-level toluene exposure

To investigate the role of strain differences in sensitivity to low-level toluene exposure on neurotrophins and their receptor levels in the mouse hippocampus, 8-week-old male C3H/HeN, BALB/c and C57BL/10 mice were exposed to 0, 5, 50, or 500 ppm toluene for 6h per day, 5 days per week for 6 weeks in an inhalation chamber. We examined the expressions of neurotrophin-related genes and receptors in the mouse hippocampus using real-time reverse transcription polymerase chain reaction (RT-PCR). The expression of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), tyrosine kinase (Trk) A, and TrkB mRNAs in the C3H/HeN mice hippocampus was significantly higher in the mice exposed to 500 ppm toluene. Among the three strains of mice, the C3H/HeN mice seemed to be sensitive to toluene exposure. To examine the combined effect of toluene exposure and allergic challenge, the C3H/HeN mice stimulated with ovalbumin were exposed to toluene. The allergy group of C3H/HeN mice showed significantly elevated level of NGF mRNA in the hippocampus following exposure to 50 ppm toluene. Then, we also examined the expression of transcription factor, dopamine markers and oxidative stress marker in the hippocampus of sensitive strain C3H/HeN mice and found that the expression of CREB1 mRNA was significantly increased at 50 ppm toluene. In immunohistochemical analysis, the density of the NGF-immunoreactive signal was significantly stronger in the hippocampal CA3 region of the C3H/HeN mice exposed to 500 ppm toluene in non-allergy group and 50 ppm in allergy group. Our results indicate that low-level toluene exposure may induce up-regulation of neurotrophin-related gene expression in the mouse hippocampus depending on the mouse strain and an allergic stimulation in sensitive strain may decrease the threshold for sensitivity at lower exposure level.

The capsaicin cough reflex in patients with symptoms elicited by odorous chemicals

Patients with multiple chemical sensitivity and eczema patients with airway symptoms elicited by odorous chemicals have enhanced cough reflex to capsaicin when applying the tidal breathing method. The aims of the present study were to test whether the capsaicin induced cough reflex was enhanced when applying the single breath inhalation method in similar groups of patients with symptoms related to odorous chemicals e.g. other persons wearing of perfume; and to investigate to what extent the reporting of lower airway symptoms influenced the cough reflex. Sixteen patients fulfilling Cullen's criteria for multiple chemical sensitivity and 15 eczema patients with airway symptoms elicited by odorous chemicals were compared with 29 age-matched, healthy controls. We measured C5--the capsaicin concentration causing five coughs or more--using the single breath inhalation test. No difference was found between groups in age, body mass index or pulmonary function. The median C5 were 129 micromol/L (control group), 48 micromol/L (multiple chemical sensitivity patients), 32 micromol/L (eczema patients). The reporting of lower airway symptoms from odorous chemicals was significantly (p<0.05) correlated to increased cough reflex sensitivity to capsaicin, independent of patient group or co-existence of asthma. The results suggest that the C5 is not reliable for diagnosing MCS but C5 can be used to verify presence of lower airway symptoms related to odorous chemicals.

Mechanisms of increased airway sensitivity to occupational chemicals and odors

PURPOSE OF REVIEW

Airway symptoms induced by chemicals and odors are common problems that are also reported after contact with substances normally regarded as nontoxic. This article reviews current findings and opinions regarding mechanisms of increased airway sensitivity to occupational chemicals and odors.

RECENT FINDINGS

Individuals exposed to organic solvents during work had more nasal irritation and lower threshold to pyridine odor compared with a nonexposed control group. Six percentage of a general population in Sweden had pronounced airway chemical sensitivity and augmented capsaicin cough sensitivity, known to reflect the sensory nerve reactivity of the airways. The cough sensitivity was associated with changed levels of nerve growth factor in nasal lavage and such patients had longstanding symptoms influencing their working capacity. Positron emission tomography activation studies with several different odorants showed in patients with odor-associated symptoms an odorant-related increase in activation of the anterior cingulate cortex and cuneus-precuneus in comparison with a control group.

SUMMARY

In subgroups of individuals with airway symptoms induced by chemicals and odors, there seems to be a sustainable physiological mechanism behind the reactions. An increased vulnerability to stress cannot be neglected as a confounding factor in some sensitive individuals.

Olfactory changes among patients receiving chemotherapy

Taste and smell changes (TSCs) are known side effects of chemotherapy, but smell changes (SCs) in the absence of taste changes are understudied. This study aims to explore SCs occurring without taste changes during chemotherapy, to better understand the characteristics of such changes, and how these experiences affect patients in their daily lives. Data derives from a qualitative interview study and a cross-sectional survey of 518 patients, with all patients receiving out-patient cancer chemotherapy in Sweden. Case studies of three patients with SCs and the 8% of survey participants with SCs only are in focus. All 43 participants with exclusively SCs reported increased sensitivity to one or several odors, with no participants reporting decreased sensitivity. Those reporting SCs significantly more often reported weight gain than those reporting TSCs, with oral problems and appetite loss significantly less common in the SC group. There were no differences in reported nausea between SC and TSC groups, but nausea was more common in the SC group than in those without TSCs. The case study reports were linked to and discussed in relation to possible explanatory models for increased olfactory sensitivity. SCs increase during chemotherapy, were often unpredictable and led to emotional consequences. The participants all reported heightened sensitivity to one or several odors which could not fully be explained by the potential explanatory models of anticipatory nausea and vomiting, pseudohallucinations, or increased chemical sensitivity.

Assessment of Upper Respiratory Tract and Ocular Irritative Effects of Volatile Chemicals in Humans

Accurate assessment of upper respiratory tract and ocular irritation is critical for identifying and remedying problems related to overexposure to volatile chemicals, as well as for establishing parameters of irritation useful for regulatory purposes. This article (a) describes the basic anatomy and physiology of the human upper respiratory tract and ocular mucosae, (b) discusses how airborne chemicals induce irritative sensations, and (c) reviews practical means employed for assessing such phenomena, including psychophysical (e.g., threshold and suprathreshold perceptual measures), physiological (e.g., cardiovascular responses), electrophysiological (e.g., event-related potentials), and imaging (e.g., magnetic resonance imaging) techniques. Although traditionally animal models have been used as the first step in assessing such irritation, they are not addressed here since (a) there are numerous reviews available on this topic and (b) many rodents and rabbits are obligate nose breathers whose nasal passages differ considerably from those of humans, potentially limiting generalization of animal-based data to humans. A major goal of this compendium is to inform the reader of procedures for assessing irritation in humans and to provide information of value in the continued interpretation and development of empirical databases upon which future reasoned regulatory health decisions can be made.

Capsaicin provocation using two different inhalation devices

BACKGROUND

Sensory hyperreactivity (SHR) has been suggested as one explanation for chemically induced airway symptoms; it can be diagnosed with a capsaicin inhalation test. Previous capsaicin inhalation studies of SHR have used a Pari Boy device. This model of inhalator device has become outdated, hence it is necessary to abandon it in favour of a new device. The aim of this study was to transfer the capsaicin inhalation test using the Pari Boy device to a corresponding model using the Maxin MA3 device.

METHODS

Twenty-one patients with SHR and 44 healthy controls visited the clinic twice and underwent a randomised protocol. The participants were provoked with saline and capsaicin using one of two devices, Pari Boy and Maxin MA3. Eight patients also underwent two additional capsaicin provocations with Maxin MA3. A new series of capsaicin concentrations was chosen for Maxin MA3. The results from each device were analysed, the agreement between the two devices and the repeatability of the Maxin MA3 were evaluated.

RESULTS

Among all participants, the mean number of coughs with the Pari Boy was 5.5 (95% CI: 2.7; 8.2) after inhalation of 0.4 micromol/L capsaicin and 20.0 (95% CI: 14.1; 25.9) after 2.0 micromol/L. With the Maxin MA3, the mean number of coughs was 3.6 (95% CI: 1.3; 4.0) after 0.06 micromol/L capsaicin, and 17.8 (95% CI: 12.0; 23.6) after 0.3 micromol/L. The Maxin MA3 showed good repeatability and the agreement between the devices with the capsaicin concentrations chosen for each device was considered to be good.

Quality of life and capsaicin sensitivity in patients with airway symptoms induced by chemicals and scents: a longitudinal study

OBJECTIVE

It is common in asthma and allergy clinics to see patients presenting with upper and lower airway symptoms that are induced by chemicals and scents and not explained by allergic or asthmatic reactions. Previous studies have shown that these patients often have increased cough sensitivity to inhaled capsaicin; such sensitivity is known to reflect the airway sensory reactivity. The aim of this study was to evaluate the duration of symptoms induced by chemicals and scents and to measure health-related quality of life (HRQL) in patients with chemically induced airway symptoms. We also wished to determine and compare repeatability of the cough response to capsaicin inhalation, and to evaluate the patients' airway sensory reactivity in a long-term perspective.

PARTICIPANTS

Seventeen patients with a history of at least 12 months of airway symptoms induced by chemicals and scents were followed over 5 years with repeated questionnaires, measurements of HRQL, and capsaicin inhalation tests.

RESULTS

The symptoms persisted and did not change significantly over time, and the patients had a reduced HRQL that did not change during the 5-year period. The capsaicin sensitivity was increased at the start of the study, the cough sensitivity was long-lasting, and the repeatability of the capsaicin inhalation test was considered to be good in a long-term perspective.

CONCLUSIONS

Upper and lower airway symptoms induced by chemicals and scents represent an entity of chronic diseases, different from asthma or chronic obstructive pulmonary disease, with persistent symptoms, a reduced HRQL, and unchanged sensory hyperreactivity.

Role of the upper airways in patients with chronic cough

PURPOSE OF THE REVIEW

Chronic cough can be caused by a number of factors, including infections, rhinosinusitis, asthma and environmental stimuli. This paper reviews recent findings and opinions regarding the role played by the upper airways in chronic cough.

RECENT FINDINGS

Chronic cough has a significant impact on quality of life, which is more pronounced in women. In Western countries, the reported occurrence of rhinosinusitis in patient groups with chronic cough ranges from 8% to 81%. Allergic rhinitis is a risk factor for later development of asthma. In children, bronchiectasis is combined with upper airway abnormalities in the majority of cases. Increased expression of the capsaicin receptor subtype named 'transient receptor potential vanilloid-1', which correlates with capsaicin cough response, has been identified in patients with chronic cough. Patients with airway chemical sensitivity and chronic cough as one symptom have augmented capsaicin cough sensitivity that is related to changed levels of nerve growth factor in nasal lavage.

SUMMARY

Involvement of the upper airways in chronic cough has been confirmed in several studies. However, there are considerable differences between different health centres in the occurrence of rhinosinusitis as a cause of chronic cough. In patients with chronic cough of various causes, a neurochemical alteration in both the upper and the lower airways appears to have taken place, followed by increased cough sensitivity.

The capsaicin cough reflex in eczema patients with respiratory symptoms elicited by perfume

Respiratory symptoms elicited by perfume are common in the population but have unclear pathophysiology. Increased capsaicin cough responsiveness has been associated with the symptoms, but it is unknown whether the site of the symptoms in the airways influences this association. The aim of this study was to investigate the association between the site of airway symptoms elicited by perfume and cough responsiveness to bronchial challenge with capsaicin. 21 eczema patients with respiratory symptoms elicited by perfume were compared with 21 healthy volunteers in a sex- and age-matched case control study. The participants completed a symptom questionnaire and underwent a bronchial challenge with capsaicin. Lower, but not upper, respiratory symptoms elicited by perfume were associated with increased capsaicin cough responsiveness. Having severe symptoms to perfume (n=11) did not relate to the site of the symptoms in the airways and was not associated with increased capsaicin cough responsiveness. In conclusion, respiratory symptoms elicited by perfume may reflect local hyperreactivity related to defensive reflexes in the airways, and measurements of the capsaicin cough reflex are relevant when patients with lower respiratory symptoms related to environmental perfume exposures are investigated.

The vanilloid receptor as a putative target of diverse chemicals in multiple chemical sensitivity

The vanilloid receptor (TRPV1 or VR1), widely distributed in the central and peripheral nervous system, is activated by a broad range of chemicals similar to those implicated in Multiple Chemical Sensitivity (MCS) Syndrome. The vanilloid receptor is reportedly hyperresponsive in MCS and can increase nitric oxide levels and stimulate N-methyl-D-aspartate (NMDA) receptor activity, both of which are important features in the previously proposed central role of nitric oxide and NMDA receptors in MCS. Vanilloid receptor activity is markedly altered by multiple mechanisms, possibly providing an explanation for the increased activity in MCS and symptom masking by previous chemical exposure. Activation of this receptor by certain mycotoxins may account for some cases of sick building syndrome, a frequent precursor of MCS. Twelve types of evidence implicate the vanilloid receptor as the major target of chemicals, including volatile organic solvents (but not pesticides) in MCS.

Safety of capsaicin cough challenge testing

BACKGROUND

Capsaicin, the pungent extract of red peppers, has achieved widespread use in clinical research because it induces cough in a dose-dependent and reproducible manner. Although > 2 decades of experience has led investigators to consider capsaicin cough challenge testing a safe diagnostic modality, this issue has not been specifically addressed in the literature.

STUDY OBJECTIVES

To review the published experience with capsaicin inhalation challenge testing in terms of safety.

DESIGN

Literature review and personal communication with study authors.

SETTING

Academic medical center.

RESULTS

One hundred twenty-two published studies since 1984 described 4,833 subjects (4,374 adults, 459 children) undergoing capsaicin cough challenge, with no serious adverse events reported. Subjects included healthy volunteers as well as patients with asthma, COPD, pathologic cough, and other respiratory conditions. Minor complaints described in a small fraction of studies consisted mainly of transient throat irritation. Personal communication with the authors of > 90% of the studies confirmed an absence of any serious adverse events. Furthermore, these investigators have performed thousands of additional capsaicin challenge studies not reported in the literature, also without any associated serious adverse events.

CONCLUSIONS

A review of the 20-year clinical experience has failed to uncover a single serious adverse event associated with capsaicin cough challenge testing in humans. Given the need for better antitussive therapies, capsaicin represents a vital component of future scientific inquiry in the field of cough.

Changes in levels of nerve growth factor in nasal secretions after capsaicin inhalation in patients with airway symptoms from scents and chemicals

Patients complaining of upper and lower airway symptoms caused by scents and chemicals have previously been shown to have increased cough sensitivity to inhaled capsaicin, but the precise mechanisms behind this reaction are unknown. Hypothesizing that a neurochemical alteration related to sensory hyperreactivity (SHR) of the airway mucosa occurs, we measured levels of nerve growth factor (NGF) in nasal lavage fluid (NAL) before and after capsaicin inhalation provocations and related the capsaicin cough sensitivity to the NGF levels. Thirteen patients with SHR and 14 control subjects were provoked with capsaicin inhalation at three different doses. We measured NGF in NAL before and after provocation and recorded cough and capsaicin-induced symptoms. All subjects demonstrated a dose-dependent cough response to capsaicin inhalation, with a more pronounced effect in patients than in controls. Basal levels of NGF were significantly lower in the patient group than in the control subjects (p < 0.01). After capsaicin provocation, the patients showed a significant increase in NGF (p < 0.01), which was related to capsaicin cough sensitivity. The findings demonstrate that, in patients with airway symptoms induced by scents and chemicals, SHR is real and measurable, demonstrating a pathophysiology in the airways of these patients compared to healthy subjects.

Repeated low level formaldehyde exposure produces enhanced fear conditioning to odor in male, but not female, rats

Multiple chemical sensitivity (MCS) is an ill-defined disorder in humans attributed to exposure to volatile organic compounds. This study draws on apparent parallels between individuals with posttraumatic stress disorder (PTSD) and panic disorder and a subset of those reporting MCS, using a conditioned fear task in rats. Male and female Sprague-Dawley rats were given repeated exposure to 2 ppm formaldehyde (Form) (1 h/day x 5 days/week x 4 week) or air, and after 2-3 weeks, rats were trained on the conditioned fear task. One half of Air and Form rats were given odor (orange oil, the conditioned stimulus, CS) paired with footshock (PRD) and the other half was given the same stimuli in an unpaired manner (UNP). After 24 h, rats were placed into the same context without the CS or footshock. Male and female PRD groups demonstrated contextual freezing 5-15% of the time, while the UNP groups showed freezing 30-50% of the time, with no effect of Air or Form pretreatment. For the next 5 days, rats were placed into a novel context and tested for freezing in the absence or presence of the CS. In male rats, Form pretreatment produced a significantly greater freezing response in both UNP and PRD groups in the presence of the CS, with no differences in freezing in the absence of the CS. In female rats, no significant differences between Form pretreated rats and Air controls were observed in either the PRD or UNP groups. The increase in conditioned fear responding to the CS after Form exposure in males suggests that repeated low-level Form may act as a stressor to produce sensitized responding within olfactory/limbic pathways, and may help explain the panic-like responses observed in a subset of individuals reporting MCS. Furthermore, the male/female differences suggest a gonadal hormonal contribution to this behavior.